Forces loyal to Libya's UN-backed unity government on Sunday pushed into the last areas of Sirte held by the Islamic State (IS) group in what was the jihadists' coastal stronghold.
The IS group captured the Mediterranean city in June 2015, sparking fears they would use it as a launchpad for attacks on Europe.
Earlier this month, the pro-GNA forces seized the jihadists' headquarters in Sirte, pinning them down in a small downtown area near the sea.
"Our forces entered the last areas held by Daesh in Sirte: district number one and district number three," a spokesman for the pro-GNA forces said on Sunday, using an Arabic acronym for the IS group.
"The final battle for Sirte has started," Reda Issa said of the city 450 kilometres (280 miles) east of Tripoli.
About 1,000 pro-GNA fighters were taking part in the offensive, he said.
An AFP photographer saw several tanks and armed vehicles move towards district number one and heard gunfire and rocket explosions as they entered the northern neighbourhood.
"Fierce street battles" were taking place with pro-GNA forces using weaponry including heavy artillery, the photographer said.
At least 25 loyalists were killed Sunday and 120 wounded, a field hospital for the pro-GNA forces said.
The AFP photographer saw several wounded loyalists being evacuated to the field hospital.
The bodies of two IS fighters lay on a street inside district number one, he said, adding that black smoke was rising from both districts.
The pro-GNA forces said on Facebook the offensive came "after air strikes overnight" and as they pressed the assault the jihadists countered with car bombs.
"The Daesh gangs committed mass suicide today when they sent five car bombs and a suicide bomber to try and stop our advancing forces," a statement said without elaborating.
Since August 1, US warplanes have backed the assault to expel the IS group from Sirte, and as of August 24, they had carried out 82 strikes, according to the US Africa Command.
The AFP photographer reported no air strikes on Sunday.
The pro-GNA forces fought their way into Sirte on June 9 and two months later seized the jihadists' headquarters at the Ouagadougou conference centre.
But their advance has been slowed by snipers, suicide bombings and booby traps.
Loyalist forces are mostly militias from western cities that have sided with the unity government of prime minister-designate Fayez al-Sarraj and the guards of oil installations that IS has repeatedly tried to seize.
Ahead of Sunday's assault, they prepared their tanks for inspection, cleaned their weapons and deployed on the outskirts of Sirte and around the two districts.
"I'm cleaning my weapon... and getting it ready for the decisive battle," one fighter, Osama Mohammad Mosbah, told AFP.
"We hope that God will help us defeat them," he said of IS.
Snipers on roofs
Sirte had been tense but calm since Thursday.
But fighting erupted Saturday on the edges of district number one between the jihadists and loyalist forces armed with machineguns and rocket launchers, the AFP reporter said.
Pro-GNA snipers deployed on the roofs of buildings whose facades were still painted with the jihadists' black flag, and used binoculars to scan their surroundings for IS fighters.
More than 370 pro-GNA fighters have been killed and nearly 2,000 wounded in the battle for Sirte since May, according to medical sources. IS casualty figures are unavailable.
Analysts say that ousting the jihadists from Libya would be a symbolic boost for the country's fragile unity government but not an end to unrest in the North African nation.
The IS group could launch more scattered attacks across Libya, they say.
The jihadist group took advantage of chaos in Libya since the 2011 uprising that toppled and killed Kadhafi, where rival militias and authorities have vied for control of the oil-rich country.
A UN-brokered deal struck in December led to Sarraj's unity government taking office in the capital, but it has since struggled to fully assert its authority.
The presidential council headed by Sarraj said on Wednesday it would present a new cabinet line-up in an attempt to secure the backing of parliament.
The legislature, which rejected a previous unity government in a vote on Monday, gave the council a "final chance" and 10 days to propose a new cabinet.
Date created : 2016-08-28